When the Prophet ﷺ sat during prayer, he would place his hands on his knees and raise the finger of his right hand next to the thumb, supplicating with it, while his left hand rested on his left knee, spread out upon it.
أن النبي ﷺ لو كان إذا جلس في الصلاة وضع يديه على ركبتيه، ورفع إصبعه اليمنى التي تلي الإبهام فدعا بها، ويده اليسرى على ركبته اليسرى، باسطها عليها.
Muslim narrated it in the Book of Prayer (580) through several routes from Abdul-Razzaq, who said, Mamar informed us, from Ubaydullah bin Umar, from Nafi, from Ibn Umar, and he related it.Tirmidhi said, after citing the hadith and grading it hasan, "This is what is practiced according to some of the scholars among the companions of the Prophet ﷺ and the successors, who prefer making the gesture during the tashahhud, and this is the view of our companions" meaning the people of hadith.